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Relationship of Hydroxamic Acid Content in Maize and Resistance to Northern Corn Leaf Blight¹

A cyclic hydroxamate (2,4-dihydroxy-7-methoxy-l,4-benzoxazin-3-one; DIMBOA) recently has been implicated in the resistance of maize (Zea mays L.) to fungi and insects. In our study, a set of 13 inbreds was used to determine the relationship of concentrations of DIMBOA and resistance to northern corn leaf blight (Helminthosporium turcicum Pass).

DIMBOA concentration was estimated by the colorimettic procedure of Hamilton in plants 60 to 75 cm in height. Mean concentrations of DIMBOA ranged from 0.06 mg/g to 0.66 mg/g fresh weight. Percent leaf infection on plants at the same height ranged from 7.41 to 19.04%. A significant correlation (r =–0.61) was obtained between these two traits.

DIMBOA concentrations also were determined in root, stem, and whorl tissues from five selected inbreds at various stages of growth. At 13-cm plant height, samples from the inbreds contained uniformly high amounts of DIMBOA. The earliest acceptable separation of high and low DIMBOA lines was obtained using stem or whorl tissue from seedlings 35 to 40 cm in height. Generally those lines highest in DIMBOA at 35 to 40 cm plant height were correspondingly high in DIMBOA at the silking stage. Similarly, lines low in DIMBOA at 35 to 40-cm plant height were low in DIMBOA at the silking stage.

Key Words: Cyclic hydroxamate • Biological resistance • Zea mays L. • Disease • Helminthosporium turcicum Pass.

² Graduate research assistant and professors of plant sci., Plant Sci. Dept. U. of N. H., Durham, NH 03824.

Received for publication July 26, 1974.

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